So I had an idea jump into my head. I know it has been so many times before, but I wanted to try my hand at it. So here is the "finished" product.

Warnings for rape, blood, and death.

After last week's discovery,we tiptoed around each other. I think we had both suspected the other, but to actually find confirmation of our dark tendencies was startling. I kept expecting to find him waiting to silence me with a knife.

This week has been stressful. The discovery and my rising, unsatisfied bloodlust has only contributed. After my last unsuccessful kill, which took a while to plan, I need to find easy prey. I'll most likely go out tonight, some passing stranger will do. I also need to get out of Sherlock's sight. The mad gleam in his eyes is unnerving me.

~~SH POV~~

I never thought I would be found not on my own terms. But I should remember that he has broken all my other rules and expectations. When he came along, I had less of a need for this, he provided enough mental stimulation, but it has been building up and I cannot ignore it any longer. The control it gives me, not just observations and unraveling situations, but power and control of the situation. The life draining from their eyes. The recognition they have in their last moments that I am completely in control and they cannot change any aspect of what I am doing to them. All of it appeals to me. Some may say I do it for the prize, no denying that fact, but the fun is had in the chase. The prize is recognition of a well planned and executed hunt.

He startled me while I was in the middle of a kill. As soon as I heard the approaching footsteps I snapped me prey's neck and got ready to flee, but the rhythm of the steps was achingly familiar. My curiosity got the best of me and I stayed to see why he was here. When he walked in I saw him glance at the blood spattered on me and look me over for injuries. His face betrayed nothing, then he said "Clean up well, it wouldn't do to be tied to this set." and turned and left the room.

I quickly followed his advice and returned to Baker street after having disposed of the evidence. I find John sitting in his chair with a cup of tea per his tradition. But he avoids my gaze. I keep expecting an outburst of anger, hurt, and disgust, but there is only silence. The few times I meet his eyes, I expect betrayal. I have shown I am not as good as I acted I was. But there is no betrayal, only confusion and what looks like panic.

I start paying closer attention to John now. As far as I know, which is a lot, he has no reason to be panicked at my actions. I am curious how he knew the correct terminology. Not many understand that these killings are "sets". Now that I look closely, I notice inconsistencies I presume I overlooked in my haste to secure for myself a friend. John's reaction to blood is most unusual. It is not an aversion, like normal people, nor is it clinical, like a doctor (as he is one), though that quickly shows up (like an act), but almost like hunger and arousal. Not the reactions of a balance, sane human (who am I to judge). I remember also the unusual hours he would sometimes keep, claiming a medical emergency (Thought I would later learn from others that there was not), and an unusual theory develops. Does John share the same dark tendencies I do?

~~End SH POV~~

The night is misty. Perfect for hunting. The winding streets of London lay themselves out as my killing ground. I find a club that is still lively. There is a group of girls at the bar all of them trying to attract attention. Sluts. I think But useful anyway. No one pays attention to random strangers so this is the perfect atmosphere to find my prey. I walk up to the bar and order some gin. Several girls eye me up. I catch the eye of the blond one. Her hair should stain nicely. Dark hair does not show blood as well as blond. She walks over with an exaggerated sway in her hips. I pretend to show interest, but her form does not excite me. She immediately takes the bait and shifts closer to me. I leisurely run my hand up her arm and say something about going someplace quiet. She lowers her eyes and quietly acquiesces. Interesting. I lead her out to the empty apartment I had staked out for my previous kill, before I had run into Sherlock's scene. Amy, as that is the girls name, seems jumpy. I ask her what is wrong. Her reply startles me. This is her first time. I almost let her go, but my bloodlust rises at the opportunity to kill and maim. This is why I faked the tremor in my hand, so as not to put my unit in danger of me going berserk. If I were attracted to her, I might have taken my pleasure before killing her, but there is only one who excites me. Sherlock.

There is the sound of the front door opening. We both whirl around to face the unexpected intruder. The tall, dark silhouette is strikingly familiar. His footsteps ring loudly as he approaches us. When he enters the light, his eyes meet mine, pupils blown wide and eyes filled with lust.

"What are you doing here and who are you?" Amy's voice startles us both out of our reverie.
The figure smirks "I could ask the same of you."
"Sherlock, what are you doing? This is my set."
"Who says I can't be a part of it?" Damn. He knows how that voice affects me. Still this is my scene, and he should stay out of it.
"Do you have a death wish?" Legitimate question considering his flippant attitude about letting the Yard know when he goes to confront criminals, without
backup.
"You are a doctor." Yeah, so.
"And a soldier. I also happen to go berserk."
"..." The look of puzzlement on his face makes me want to kiss it off. Understanding dawns on his face and he asks "That is why you left the army is it not? I nod my head in agreement. I feel Amy tense, ready to run, and quickly grasp her closer. "Sherlock..." I warn him. He understands and strides to a box on the side of the room. He then approaches Amy with a length of rope. She starts struggling when she sees it, but my grip on her does not relent.

"How do you want her?" Sherlock calmly asks me. The question startles me. The smirk on his face clues me into the fact that he knew I was mesmerized by his shadowed form striding toward me. He cocks his eyebrow in a question and I remember his inquiry.
"Kneeling, hands behind her back."
We quickly set to work. She looks so fragile, kneeling alone on the floor, pulse racing. Sherlock walks up behind me and presses his front to my back.
"Now what John?" he purrs in my ear. "You have both of us now." The thought excites me. I reach back and roughly tug his head down to whisper in his ear.
"She is a virgin." I shut my mouth, startled. What did I just blurt out? Why? Oh well. The gleam I notice in his eye makes me wary. It never bodes well. His voice rough with arousal, Sherlock breathes out "I want to see you take her, and when you climax, slit her throat."

I am startled. I've come to terms with being a killer, but never have I considered the other crimes. My rapid stiffening and swift intake of breath alerts Sherlock to my inner turmoil.

"You have never forcibly taken pleasure from someone?"

"I'm not that kind of person." It is true. I am not. It was bad enough to come to terms with my violent side. I thought being a doctor would suppress or temper it, but then I ruined the chance by joining the army. Then, with the combined knowledge of medical school and military training, I became deadly. Twice on the field I went berserk, but it was ignored or toned down in reports. I worked to contain and repress the bloodlust and need for causing pain, but I was good at hiding in plain sight and covering my tracks, so I discovered how to expend it without endangering my unit. Doing so helped for a time, but it was like using a bandaid on a gaping bullet wound. Then when I got shot, I saw a way out, and so I took it.

"Well then John. Let me teach you the pleasures of our trade."
"No." This is final. I promised myself I would stay away from the slippery slope of the criminal underworld.

Sherlock has a look of determination on his face and I know it doesn't bode well for me. He nips at the skin right below my ear and shivers run down my spine.

"I'm asking you to." He purrs and my resolve wavers.
"No Sherlock. I am a killer, and a killer only. I do not do rape." He harrumphs. His hands start running up and down my arms. He presses himself more fully against me and I feel his prominent erection pressing into my lower back.
"Come on John" he almost whines, but with his voice it is impossible, "When you take, there is no concern for the other being taken from. You can do whatever you want." The melody of his voice flows over me. His words though not powerful, in combination with his voice can be deadly. He croons his siren's song into my ear, and I feel the walls of my resolve crumble into dust.
"Fine, Sherlock. Be it in your head."
We both then turn to look at Amy's lonesome, fragile figure. She sees our gazes and tries harder to break the bonds. I turn to Sherlock and ask.
"What will you do?"
"Whatever you want."

His words have made me painfully turned on. I walk over to Amy and yank her head up by her hair, the gag cutting into the sides of her mouth.
"Sherlock" I call, "is there a table or bench around here?" He goes to the other room and pulls out a low work table. We lift Amy up onto it with Sherlock standing at her head and myself at her feet. I spread her legs and wrap them around my waist while Sherlock holds her arms down. I bring out the bayonet I reserve for these types of scenes. Both pairs of eyes widen, one in fear, the other in excitement. I motion to Sherlock to lift her gag up as I hold the blade at her throat. Relieved of her gag, Amy opens her mouth to shout, but stops at the feel of the bayonet pressing on her jugular.
"Do you know what is going to happen to you?"
"You... you're... you're gonna... rape me?" She stutters out.
Sherlock chuckles "If you wish." and swiftly replaces the gag. The look of pure and absolute panic on her face is delicious and I can't wait to see that expressive face when she realizes what is actually going to happen.

I lift up Amy's shirt with the tip of the blade and slowly rip it from bottom to top. Sherlock's fingers slowly spread it open. Her pale torso covered only in a simple black bra, stretches out before us like a blank canvas. I start tracing her ribs with the bayonet, scratching the skin, but not drawing blood - yet.

I start fiddling with the clasp on her skirt and Amy lets out a low whimper of fear. I yank it open just to hear more of that addicting sound.
"Sherlock, bind her arms to the table and come over here."

He slowly unclasps his belt and draws them out of his belt loops. This draws my eye to the erection that is painfully visible through his trousers. He catches me looking, smirks again, and I can't wait much longer.
"Come over here." I growl. He slinks over, all sleek lines and predatory elegance. As soon as he is within arms reach I grasp the back of his head and shove him to his knees in front of me.
"Get me nice and wet so I can fuck this bitch, or I might just fuck you, dry." his eyes widen at my words and I see him shiver in arousal. The whimpers and cries of Amy only adds to it.

Sherlock and I slowly kiss sharing the taste of blood from the mangled body cooling behind us. I slowly run my hand through his thick hair.
"I didn't hurt you, did I?"
"God no, John." He picks up my and and sucks each finger clean, one by one. He arouses me so much. I can't help it and pull him into a rough and dirty kiss. I breathlessly tell him.
"Lets clean up and go to Baker Street. I can reward you there if you want." Sherlock only grins at me and shivers go down my spine. We'll have to do this again.

Let these dark tendencies bind us and let us revel in this madness.

So, here you go. My first attempt at dark John. Not sure how it turned out. Please review and let me know how it is, what I can improve on.

FYI: I have posted this on AO3, where I also will post the full sex scene once it is completed.